Wild gorillas take time for tool use.

On Oct. 9, 2004, a group of researchers studying gorillas in northern Congo happened upon a never-before-seen event. In a swampy forest clearing, a female gorilla yanked a roughly 3-foot-long branch from a dead tree and waded into a deep pool of water. Keeping the stick in front of her and her upper body above water, the gorilla slowly advanced about 30 feet into the pool as she tested the water's depth. Then, she returned to shore to comfort her wailing infant.

The scientists, led by Thomas Breuer of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, had for the first time witnessed and photographed tool use by a wild gorilla.

About 6 weeks later, Breuer and his colleagues recorded a second instance of such behavior. Another female gorilla ripped the thick trunk off a dead shrub. She used the piece of wood to support herself with one hand while digging for herbs with the other. Then, she placed the trunk across a patch of swampy ground and used it as a makeshift bridge.

The investigators report their observations in the November PloS Biology. Until now, they say, only chimpanzees and orangutans, among nonhuman primates, have been observed using tools in the wild.--B.B.